A conventional valve device is known, which includes an annular valve seat elastically supported by a casing, a ball valve having a ball surface shaped in a convex sphere surface in sliding contact with a sealing surface of the valve seat, and an elastic component which biases the valve seat against the ball surface of the ball valve (for example, Patent Literature 1).
The valve device controls the communication state between a first opening of the valve seat and a second opening of the ball valve by rotating the ball valve with a drive unit, so as to control the opening-and-closing operation of the ball valve.
However, in the conventional valve device, since the sealing surface of the valve seat and the ball surface of the ball valve are always in sliding contact to open and close, the sealing surface is worn out, such that the contact surface between the sealing surface and the ball surface increases. For this reason, the contact surface pressure of the sealing surface relative to the ball valve falls, and fluid may leak easily. In other words, the sealing performance for the fluid at the valve closed time of the ball valve cannot be secured over a long period of time.
Therefore, a valve device is required to achieve both of improvement in wear-resistant of the sealing surface of the seat and improvement in reliability of restricting fluid leak while the seat is pressed against the valve by the biasing force of the elastic component.